This invention relates to draw tape bags made from thermoplastic materials. More particularly it relates to processes for making such bags and the bags produced thereby wherein the drawtape material is formed integrally with the material of the bag body.
Draw tape and draw string bags are well known. For example, U.S. Pat. Nos. 1,861,864, 1,920,824, 2,777,491 and 2,799,611 disclose a variety of draw string bags and manufacturing methods. Draw string bags made of thermoplastic materials have also been known. See U.S. Pat. Nos. 3,029,853, 3,114,497 and 3,283,994.
In producing draw tape bags of thermoplastic material, it has been customary to form the draw tape material independent of the bag wall material, and later insert the draw tape into a hem as the hem was formed. See U.S. Pat. Nos. 4,493,683, 4,786,191 and 4,792,241. One improvement in the bag formation process is to make the draw tape at the same time as the bag wall material, and thus eliminate the need for draw tape storage rolls, etc. U.S. Pat. No. 3,196,757 to Samways (incorporated herein by reference) discloses an embodiment in which a tubular film is formed, pleated and slit such that ribbons of web material slit from the bag mouth forming margins are used to form the draw tapes for the bag, and are channeled into hems in the usual manner.
The present invention provides a further improvement to such a integral draw tape and bag forming process. Since the draw tape disclosed in the process of U.S. Pat. No. 3,196,757 is made of the same material as the bag wall, the strength of the draw tape and strength of the bag wall are necessarily related. If a stronger draw tape is desired, the bag wall thickness could be increased, or the entire bag structure could be formed from a resin having greater strength properties. The costs associated with either solution, however, may not be justified, since a suitable strong bag may be formed of the thinner or lower cost material.
Thus, a simple manufacturing process which produces a thermoplastic draw tape bag in which the draw tape strength properties are independent of the strength of the rest of the bag, yet still allowing integral formation of the draw tape and the bag material, is a significant invention.